Prokaryotic expression system and methods of using the same

1 . A composition comprising a synthetic major ampullate spidroin protein (MaSp)-based polymer in the form of particles having an average size in the range of 0.5 μm to 1.5 μm; wherein said MaSp-based polymer is a MaSp1 protein comprising a single N-terminal region, a single C-terminal region and a repetitive region comprising 10-20 repeats, wherein at least one of: (i) each of said repeats is between 5 and 60 amino acids long; and (ii) each of said repeats has at least 70% homology to a repetitive sequence derived from the repetitive region of Araneus diadematus fibroin 4 (ADF4) protein,

wherein the repetitive region of the ADF4 protein comprises the amino acid sequence as set forth in SEQ ID NO: 1 (AAAAAAASGSGGYGPENQGPSGPVAYGPGGPVSSAAAAAAAGSGPGGYGPENQ GPSGPGGYGPGGSGSSAAAAAAAASGPGGYGPGSQGPSGPGGSGGYGPGSQGPSG PGASSAAAAAAAASGPGGYGPGSQGPSGPGAYGPGGPGSSAAASGPGGYGPGSQ GPSGPGGSGGYGPGSQGPSGPGGPGASAAAAAAAAASGPGGYGPGSQGPSGPGA YGPGGPGSSAAASGPGGYGPGSQGPSGPGAYGPGGPGSSAAAAAAAGSGPGGYG PGNQGPSGPGGYGPGGPGSSAAAAAAASGPGGYGPGSQGPSGPGVYGPGGPGSSA AAAAAAGSGPGGYGPGNQGPSGPGGYGPGGSGSSAAAAAAAASGPGGYGPGSQ GPSGPGGSGGYGPGSQGPSGPGASSAAAAAAAASGPGGYGPGSQGPSGPGAYGPG GPGSSAAASGPGGYGPGSQGPSGPGAYGPGGPGSSAAAAAAASGPGGYGPGSQGP SGPGGSRGYGPGSQGPGGPGASAAAAAAAAASGPGGYGPGSQGPSGPGYQGPSG PGAYGPSPSASAS).

2 . The composition of claim 1 , wherein at least one of: said particles are porous particles and are characterized by BET surface area of at least 10 m 2 /g; and said MaSp-based polymer is characterized by a DSC pattern exhibiting at least an endothermic peak in the range of from 200° C. to 280° C.

3 . The composition of claim 1 , further comprising an additional compound in contact with said MaSp-based polymer, and wherein said additional compound is selected from a biologically active agent, cosmetically active ingredient and a nutraceutical.

4 . The composition of claim 3 , wherein a weight per weight (w/w) ratio of said MaSp-based polymer to said additional compound is between 10:1 and 1:10.

5 . The composition of claim 1 , wherein each of said repeats comprises the amino acid sequence as set forth in any one of: SEQ ID NO: 2 (SGPGGYGPGSQGPSGPGGYGPGGPGSS) and SEQ ID NO: 3 (AAAAAAAASGPGGYGPGSQGPSGPGGYGPGGPGSS) or a variant having at least 90% sequence identity thereto.

6 . The composition of claim 1 , wherein said repetitive region comprises 10-20 repeats of SEQ ID NO: 3; and wherein said MaSp-based polymer is a water insoluble polymer.

7 . The composition of claim 1 , wherein said single N-terminal region consists of: SEQ ID NO: 4 (MSYYHHHHHHDYDIPTTENLYFQGAMDPEFKGLRRRAQLV); and wherein said single C-terminal region consists of: SEQ ID NO: 7 (VAASRLSSPAASSRVSSAVSSLVSSGPTNGAAVSGALNSLVSQISASNPGLSGCD ALVQALLELVSALVAILSSASIGQVNVSSVSQSTQMISQALS).

8 . The composition of claim 1 , obtained by expression of MaSp in a bacterium.

9 . A composition comprising the MaSp-based polymer of claim 1 non-covalently bound to an additional polymer, wherein a w/w ratio of said MaSp-based polymer to said additional polymer is between 1:1 and 1:100.

10 . The composition of claim 9 , wherein a w/w concentration of said additional polymer is 50% to 95% (w/w) of the total composition.

11 . The composition of claim 9 , wherein said additional polymer is selected from a synthetic polymer, a thermoplastic polymer, a thermoset, a film forming agent, an epoxy, a polyester a polyamide, a polyol, a polyurethane, polyethylene, a silicon, liquid crystal polymers, maleic anhydride grafted polypropylene, a polyacrylate, a polycarbonate, polyamides, Nylon 4,6, Nylon 6, Nylon 6,6, Nylon 11, Nylon 12, poly(arylamide), polyethylene, polybutylene terephthalate, polyethylene terephthalate, polyphenylene sulfide, polyphthalamide, polypropylene, poly(vinylidene fluoride), Poly(2-hydroxyethyl methacrylate) (pHEMA), polyurethane, polyvinyl butyral, ethylene vinyl alcohol copolymer, polylactide acid (PLA) or a copolymer thereof, polycaprolactone (PCL), xanthan, cellulose, collagen, elastin, keratin, cotton, rubber, cellulose, wool, and any combination thereof.

12 . The composition of claim 10 , wherein a w/w ratio between said film forming agent and said MaSp based fiber is from 5:1 to 50:1.

13 . The composition of claim 9 , characterized by at least one improved mechanical property as compared to the property for the additional polymer free of said MaSp-based polymer, wherein said property is selected from the group consisting of: Young's modulus, storage modulus, loss modulus, tensile strength, fracture strain, yield point, toughness, work to failure, impact strength, tear strength, flexural modulus, flexural strain and stress at a specific percentage elongation, and abrasion.

14 . An article comprising the composition of claim 1 , being in a form of film, a suture, surgical mesh, medical adhesive strips, electrospun mesh, skin grafts, fat grafts, cosmetics, dermal fillers, drug eluting/delivery device, replacement ligaments, clothing fabric, bullet-proof vest lining, cable, tube, film, rope, fishing line, tires, sports equipment, and reinforced plastics.

15 . A recombinant bacterium having the ability to express a MaSp-based polymer comprising the amino acid sequence as set forth in SEQ ID NO: 2 (SGPGGYGPGSQGPSGPGGYGPGGPGSS).

16 . A process, comprising:

(i) providing the recombinant bacterium of claim 15 ;

(ii) providing conditions for expression of the MaSp by the bacterium;

(iii) isolating the expressed proteins, and optionally,

(iv) drying of said synthetic dragline spider silk

thereby fabricating the synthetic dragline spider silk.

17 . The process of claim 16 , wherein said step (ii) comprises one or more of: (a) providing a solution with a pH in the range of 5 to 6.5; (b) providing an expression inducer; (c) waiting during a period of time to obtain an insoluble polymer.

18 . The process of claim 16 , further comprising an enrichment step with an additional polymer comprises mixing a solution of said synthetic dragline spider silk, with solution of said additional polymer.